This invention relates to a method of preparing a prepreg, a prepreg, a metal clad laminated board and a printed wiring board.
In general, a prepreg to be used for a printed wiring board is prepared by impregnating a thermosetting resin varnish in which a thermosetting resin is diluted by an organic solvent into a glass woven fabric or glass non-woven fabric, and then, vaporizing the solvent in a drying oven to cure the thermosetting resin to a B-stage state. These impregnation process and the drying step are a series of steps in an impregnation machine, and the thermosetting resin varnish is impregnated into a belt-shaped glass woven fabric or glass non-woven fabric, and the impregnated glass woven fabric or glass non-woven fabric is dried in a drying oven.
The impregnation process of impregnating the thermosetting resin varnish into a glass woven fabric or glass non-woven fabric is to carry out by immersing the glass woven fabric or glass non-woven fabric into the thermosetting resin varnish, and then, passing the impregnated material through the gap of squeeze rolls to measure an amount of the thermosetting resin varnish.
In the drying step in which the solvent is vaporized and the resin is cured, a vertical type drying oven is generally used in the case of the glass woven fabric or glass non-woven fabric. It has been generally carried out that, after impregnating the thermosetting resin varnish into a substrate to be conveyed, the impregnated material is passed through the gap of squeeze rollers to the vertical direction, and moved by tensile force of drawing rollers at the outlet of the drying oven in the vertical type drying oven to the vertical direction, and the resin is cured to a B-stage state.
However, in the above-mentioned vertical type drying oven, when the glass woven fabric or glass non-woven fabric impregnated with the thermosetting resin varnish is dried, it is necessary to move the glass woven fabric or glass non-woven fabric at upward, and for moving the glass woven fabric or glass non-woven fabric, a large tension is required. That is, in the vertical type drying oven, a tension is required to move the glass woven fabric or glass non-woven fabric to upward contrary to gravity and the tension is to be acted on the glass woven fabric or glass non-woven fabric by drawing rolls provided at the outlet of the vertical type drying oven. Since the resin is cured while applying the tension thereto, the tension is remained in the prepreg as a strain.
When a metal clad laminated board is prepared by using the prepreg having the residual strain, the residual strain causes bad effects and there is a problem that dimensional stability or warp characteristic of the metal clad laminated board is lowered. Also, when the prepreg is used as a prepreg for adhering multiple layers, the same problem arises.
The present invention has accomplished to solve the above-mentioned problems, and an object thereof is to provide a method of preparing a prepreg having a little residual strain, the prepreg prepared by the preparation method, and a metal clad laminated board and a printed wiring board using the same, which have high dimensional stability.
The present invention relates to the following method of preparing a prepreg and a prepreg prepared by the same, and a metal clad laminated board and a printed wiring board using the same.
1. A method of preparing a prepreg comprising the steps of a impregnation process in which a thermosetting resin varnish is impregnated into a fiber base material and a drying step in which a solvent of the impregnated thermosetting resin varnish in the fiber base material is vaporized and the resin is semi-cured, wherein said drying step is carried out by moving the fiber base material into which the thermosetting resin varnish is impregnated with a tensile force of 3.0 N/cm or less.
2. A method of preparing a prepreg comprising the steps of a impregnation process in which a thermosetting resin varnish is impregnated into a fiber base material and a drying step in which a solvent of the impregnated thermosetting resin varnish in the fiber base material is vaporized and the resin is semi-cured, wherein the drying step is carried out by moving the fiber base material into which the thermosetting resin varnish is impregnated to a horizontal direction.
3. A method of preparing a prepreg comprising the steps of a impregnation process in which a thermosetting resin varnish is impregnated into a fiber base material and a drying step in which a solvent of the impregnated thermosetting resin varnish in the fiber base material is vaporized and the resin is semi-cured, wherein the drying step is carried out by using a horizontal drying oven with a temperature at an inlet portion of the drying oven lower than a softening point of the resin.
4. A method of preparing a prepreg comprising the steps of a impregnation process in which a thermosetting resin varnish is impregnated into a fiber base material and a drying step in which a solvent of the impregnated thermosetting resin varnish in the fiber base material is vaporized and the resin is semi-cured, wherein the drying step is carried out by moving the fiber base material into which the thermosetting resin varnish is impregnated to a horizontal direction, and by heating the fiber base material firstly at a temperature lower than a softening point of the resin.
5. A method of preparing a prepreg comprising the steps of a impregnation process in which a thermosetting resin varnish is impregnated into a fiber base material and a drying step in which a solvent of the impregnated thermosetting resin varnish in the fiber base material is vaporized and the resin is semi-cured, wherein the drying step is carried out by using a horizontal drying oven having gas injection nozzles in the drying oven provided at top and bottom alternately.
6. A method of preparing a prepreg comprising the steps of a impregnation process in which a thermosetting resin varnish is impregnated into a fiber base material and a drying step in which a solvent of the impregnated thermosetting resin varnish in the fiber base material is vaporized and the resin is semi-cured, wherein the drying step is carried out by moving the fiber base material into which the thermosetting resin varnish is impregnated to a horizontal direction, and the fiber base material is supported by blowing a gas from top and bottom alternately to the fiber base material and stabilized.
7. The method of preparing a prepreg according to the above 1 to 6, wherein a tensile force A to move the fiber base material, a gas injecting force B to support the base material and a combined force F thereof have the relationship that an angle xcex8 formed by the tensile force A and the combined force F is 18 to 60xc2x0.
8. The method of preparing a prepreg according to any one of the above 1 to 7, wherein the fiber base material into which the thermosetting resin varnish is impregnated is passed through the drying oven in the drying step.
9. The method of preparing a prepreg according to any one of the above 1 to 8, wherein the fiber base material is a belt-shaped material.
10. The method of preparing a prepreg according to any one of the above 1 to 9, wherein a difference between a prepreg dimension y (mm) and a fiber base material width dimension x (mm) as a starting material satisfies the equation (1):
0.3(%)xe2x89xa7(xxe2x88x92y)/xxc3x97100xe2x80x83xe2x80x83(1). 
11. The method of preparing a prepreg according to any one of the above 1 to 10, wherein the fiber base material is a glass woven fabric or a glass non-woven fabric.
12. The method of preparing a prepreg according to any one of the above 1 to 11, wherein the fiber base material comprises a woven fabric and a relationship between a gas permeability q (cc/cm2/sec) and a thickness z (xcexcm) satisfies the equation (4):
qxe2x89xa6xe2x88x920.1z+25xe2x80x83xe2x80x83(4). 
13. The method of preparing a prepreg according to any one of the above 1 to 11, wherein the fiber base material comprises a non-woven fabric and its weighing is 30 to 100 g/m2.
14. A prepreg prepared by any one of the methods according to any one of the above 1 to 13.
15. A metal clad laminated board which comprises the prepreg according to the above 14 or a laminated material thereof and a metal foil laminated on at least one surface of the above material under heating and pressure, and subjected to molding.
16. A printed wiring board which comprises applying a circuit processing to the metal clad laminated board according to the above 15.